Abstract
Tree rings provide information about the climatic conditions during the growing season by recording them in different anatomical features, such as intra-annual density fluctuations (IADFs). IADFs are intra-annual changes of wood density appearing as latewood-like cells within earlywood, or earlywood-like cells within latewood. The occurrence of IADFs is dependent on the age and size of the tree, and it is triggered by climatic drivers. The variations of IADF frequency of different species and their dependence on climate across a wide geographical range have still to be explored. The objective of this study is to investigate the effect of age, tree-ring width and climate on IADF formation and frequency at a regional scale across the Mediterranean Basin in Pinus halepensis Mill., Pinus pinaster Ait., and Pinus pinea L. The analyzed tree-ring network was composed of P. pinea trees growing at 10 sites (2 in Italy, 4 in Spain, and 4 in Portugal), P. pinaster from 19 sites (2 in Italy, 13 in Spain, and 4 in Portugal), and P. halepensis from 38 sites in Spain. The correlations between IADF frequency and monthly minimum, mean and maximum temperatures, as well as between IADF frequency and total precipitation, were analyzed. A significant negative relationship between IADF frequency and tree-ring age was found for the three Mediterranean pines. Moreover, IADFs were more frequent in wider rings than in narrower ones, although the widest rings showed a reduced IADF frequency. Wet conditions during late summer/early autumn triggered the formation of IADFs in the three species. Our results suggest the existence of a common climatic driver for the formation of IADFs in Mediterranean pines, highlighting the potential use of IADF frequency as a proxy for climate reconstructions with geographical resolution.
Highlights
Tree-ring width is a powerful proxy of past environmental conditions able to record fluctuations of biotic and abiotic factors during the tree’s lifetime (Fritts, 2001)
In order to reach this aim, we investigated the relationships between intra-annual density fluctuations (IADFs) frequency and tree-ring age, tree-ring width and climate in three widespread Mediterranean pine species, namely P. halepensis, P. pinaster and P. pinea, growing along their distribution ranges
Our results showed that tree-ring age has to be taken into account when analyzing IADFsclimate relationships because it plays an important role in IADF formation in Mediterranean pines
Summary
Tree-ring width is a powerful proxy of past environmental conditions able to record fluctuations of biotic and abiotic factors during the tree’s lifetime (Fritts, 2001). IADFs are defined as a layer of cells within a tree ring identified by different shape, size, and wall thickness (Kaennel and Schweingruber, 1995), and characterized by the occurrence of latewood-like cells within earlywood or earlywood-like cells within latewood (Fritts, 2001). They can occur in several species in different environments and are often irregularly found in time and space (Cherubini et al, 2003; De Micco et al, 2016). The expected climate changes will likely have an impact on tree growth and IADF frequency
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